Acyl germanium photoinitiators and process for the preparation thereof

Abstract

Acyl germanium compound according to general formula [R.sub.mAr(CO)].sub.4Ge and process for the preparation thereof. The compound is suitable as initiator for radical polymerization.

Claims

1. Acyl germanium compound according to general formula (I),
[R.sub.mAr(CO)].sub.4-Ge(I) in which the variables have the following meanings: Ar a mono- or polycyclic hydrocarbon radical with 6 to 18 ring-carbon atoms, which can be substituted m times by the R group and which can contain one or more heteroatoms in the ring, wherein m is an integer from 0 to 6 and cannot be greater than the number of substitutable hydrogen atoms in Ar, R is halogen, NR.sup.1.sub.2, OH, OSiR.sup.2.sub.3, (CO)R.sup.3, CN, NO.sub.2, CF.sub.3, COOR.sup.4, or a C.sub.1- to C.sub.20-alkyl, -alkenyl, -alkoxy or -alkenoxy radical, which can be linear, branched or cyclic, which can be interrupted by one or more O atoms and which can contain a radically polymerizable group, or O, wherein R.sup.1-R.sup.3 independently of each other are in each case H or a linear or branched C.sub.1- to C.sub.12-alkyl radical and R.sup.4 is H, a linear or branched C.sub.1- to C.sub.12-alkyl radical or SiR.sup.5.sub.3, wherein R.sup.5 is a linear or branched C.sub.1- to C.sub.10-alkyl radical.

2. Acyl germanium compound according to claim 1, in which the variables have the following meanings: Ar an aromatic C.sub.6-C.sub.10 radical, which can be substituted m times by R, wherein m is an integer from 1 to 3 and R is Cl, NR.sup.1.sub.2, OSiR.sup.2.sub.3, (CO) R.sup.3, CN, NO.sub.2, CF.sub.3, COOR.sup.4, or a C.sub.1- to C.sub.10-alkyl, -alkenyl, -alkoxy or -alkenoxy radical, which can be linear, branched or cyclic, which can be interrupted by one or more O atoms, and which can contain a radically polymerizable group, wherein R.sup.1-R.sup.3 independently of each other are in each case H or a linear or branched C.sub.1- to C.sub.8-alkyl radical and R.sup.4 is H, a linear or branched C.sub.1- to C.sub.8-alkyl radical or SiR.sup.10.sub.3 and R.sup.5 is a linear or branched C.sub.1 to C.sub.5 alkyl radical.

3. Acyl germanium compound according to claim 1, in which the variables have the following meanings: Ar a phenyl radical, pyridyl radical, naphthyl radical, anthryl radical, anthraquinone-yl radical, which can be substituted m times by R, wherein m is an integer from 1 to 3 and R is NR.sup.1.sub.2, CN, NO.sub.2, CF.sub.3, a C.sub.1- to C.sub.3-alkyl radical or C.sub.1- to C.sub.3-alkoxy radical, wherein R.sup.1 is H or a linear C.sub.1- to C.sub.3-alkyl radical.

4. Composition which, relative to its total mass contains 0.001 to 5 wt. % of an acyl germanium compound of Formula (I) according to claim 1 and at least one polymerizable binder.

5. Composition according to claim 4 which contains as polymerizable binder at least one radically polymerizable monomer and/or prepolymer.

6. Composition according to claim 5, which contains as binder at least one mono- or multifunctional (meth)acrylate or a mixture thereof.

7. Composition according to claim 4, which contains 0.001-5 wt. % acyl germanium compound of Formula (I), 10 to 99.9 wt.-% polymerizable binder, 0 to 85 wt.-% filler, relative in each case to the total mass of the composition.

8. Process of using an acyl germane according to Formula (I) as initiator for radical polymerization, wherein Formula (I) comprises
[R.sub.mAr(CO)].sub.4-Ge(I) in which the variables have the following meanings: Ar a mono- or polycyclic hydrocarbon radical with 6 to 18 ring-carbon atoms, which can be substituted m times by the R group and which can contain one or more heteroatoms in the ring, wherein m is an integer from 0 to 6 and cannot be greater than the number of substitutable hydrogen atoms in Ar, R is halogen, NR.sup.1.sub.2, OH, OSiR.sup.2.sub.3, (CO)R.sup.3, CN, NO, CF.sub.3, COOR.sup.4, or a C.sub.1- to C.sub.20-alkyl, -alkenyl, -alkoxy or -alkenoxy radical, which can be linear, branched or cyclic, which can be interrupted by one or more O atoms and which can contain a radically polymerizable group, or O, wherein R.sup.1-R.sup.3 independently of each other are in each case H or a linear or branched C.sub.1- to C.sub.12-alkyl radical and R.sup.4 is H, a linear or branched C.sub.1- to C.sub.12-alkyl radical or SiR.sup.5.sub.3, wherein R.sup.5 is a linear or branched C.sub.1- to C.sub.10-alkyl radical.

9. Acyl germanium compound according to claim 2, wherein the radically polymerizable group comprises vinyl, methacrylate, (meth)acrylamide or N-alkylacrylamide, and wherein the radically polymerizable group in the case of non-cyclic radicals is terminal.

10. Acyl germanium compound according to claim 3, wherein R is linear and can bear a terminal radically polymerizable group comprising vinyl, acrylate, methacrylate.

Description

(1) The invention is described in further detail in the following with reference to examples.

Example 1

(2) Synthesis of Tetrabenzoyl Germane (TBGe)

(3) ##STR00006##

a) Synthesis of tetrakis(trimethylsilyl)germane [(Me3Si)4Ge]

(4) 10.00 g (1.4 mol) lithium was placed in a flask with a dropping funnel and pressure equalizer, and 300 mL dry THF was added. Trimethylchlorosilane (95 ml, 0.75 mol) was rapidly added dropwise and stirred for 10 min. at 78 C. Germanium tetrachloride (21 ml, 0.19 mol, 1:5 diluted in THF) was then added very slowly dropwise at 78 C. (ca. 2 h). Once the addition had ended the reaction solution was heated to room temperature and stirred for a further 12 hours. For working up the reaction mixture was first filtered through Celite and then poured onto 1 M H.sub.2SO.sub.4/ice. After phase separation in the dropping funnel the aqueous phase was extracted 3 times with diethylether, the combined organic phases were dried over anhydrous Na.sub.2SO.sub.4, filtered and the solvent was removed in a rotavapor. For purification the crude product was sublimated (p<5 mbar; T>150 C.). The yield after sublimation was 26.8 g (Me.sub.3Si).sub.4Ge (42%).

(5) NMR spectroscopy: .sup.1H(CDCl.sub.3) [ppm]=0.24 (s, Si(CH.sub.3).sub.3). .sup.29Si (CDCl.sub.3): [ppm]=5.33 (SiMe.sub.3).

b) Synthesis of tetrabenzoyl germane (TBGe)

(6) 3.00 g (8.21 mmol; 1.00 eq.) Tetrakistrimethylsilyl germane and 1.01 g KOtBu (9.03 mmol; 1.1 eq.) were weighed into a Schlenk flask and dissolved in 20 ml ethylene glycol dimethyl ether (DME). The reaction was complete when the reaction solution had a clear yellow to orange colour. After approximately one hour 4.18 g (33.66 mmol, 4.1 eq.) benzoyl fluoride was added by means of a syringe. The reaction solution became black and, after the addition was complete, orange. The reaction solution was then stirred overnight at room temperature. After aqueous working up with 3% H.sub.2SO.sub.4 the phases were separated and the aqueous phase extracted 3 times with diethyl ether. The combined organic phases were dried over anhydrous sodium sulphate and the volatile components removed in a rotary evaporator. The obtained crude product was recrystallized from acetone and 1.70 g pure tetrabenzoyl germane (42%) was obtained as a crystalline, yellow solid (melting point: 82.5-83.0 C.). NMR spectroscopy: .sup.1H (CDCl.sub.3): [ppm]=7.99-7.96 (m, 2H, aryl-H), 6.84-6.82 (m, 3H, aryl-H). .sup.13C (CDCl.sub.3): [ppm]=222.01 (GeCOPh), 140.57 (aryl-Cl), 133.81 (aryl-C2), 129.15 (aryl-C3), 128.77 (aryl-C4).

(7) UV-VIS spectroscopy: [nm]( [L mol.sup.1 cm.sup.1])=403 (1240), 419sh (1050).

(8) IR spectroscopy: [cm.sup.1]=1639, 1617 (m, C=O); 1590, 1574, 1444 (m, CC); 880, 762, 673 (s, CH).

Example 2

Synthesis of tetrakis(2,4,6-trimethylbenzoyl)germane (TMGe)

(9) ##STR00007##

(10) 2.77 g (7.66 mmol; 1.00 eq.) (Me.sub.3Si).sub.4Ge and 0.94 g KOtBu (8.4 mmol; 1.1 eq.) were weighed into a Schlenk vessel and dissolved in 15 ml DME. The reaction was complete when the reaction solution had a clear yellow to orange colour. After approximately one hour the obtained solution was slowly added dropwise to a solution, cooled to 78 C., of 1.66 g (0.91 mmol, 1.2 eq.) 2,4,6-trimethylbenzoyl chloride in 80 ml diethyl ether and the obtained mixture stirred overnight at room temperature. After aqueous working up with 3% H.sub.2SO.sub.4 the phases were separated and the aqueous phase extracted 3 times with diethyl ether. The combined organic phases were dried over anhydrous sodium sulphate and the volatile components removed in a rotary evaporator. The formed crude product with a mass of 3.85 g contained 36% tetraacyl germanium and 64% monoacyl germanium compound and was separated by column chromatography over silica gel (gradient: heptane, toluene). Recrystallization from acetone was then carried out, and 1.58 g (24%) tetrakis(2,4,6-trimethylbenzoyl)germane was obtained as a crystalline, yellow solid (melting point: 198-199 C.).

(11) NMR spectroscopy: .sup.1H (CDCl.sub.3): [ppm]=6.57 (s, 2H, Aryl-H), 2.24 (s, 3H, para-CH.sub.3), 2.06 (s, 6H, ortho-CH.sub.3). .sup.13C (CDCl.sub.3): [ppm]=233.40 (GeCOMes), 141.60 (aryl-Cl), 139.26 (aryl-C2), 132.88 (aryl-C3), 128.53 (aryl-C4), 21.15 (para-CH.sub.3), 19.13 (ortho-CH.sub.3).

(12) UV-VIS spectroscopy: [nm]([L mol.sup.1 cm.sup.1])=288 (17428), 376 (1475).

(13) IR spectroscopy: [cm.sup.1]=2917 (w, .sub.asCH.sub.3); 1639, 1608 (m, C=O); 1202 (m, .sub.asCH.sub.3); 833, 609 (m, CH.sub.3).

Example 3

Preparation of Light-Curing Resins Using Tetrabenzoyl Germane (TBGe) or tetrakis(2,4,6-trimethylbenzoyl)germane (TMGe) from Examples 1 and 2

(14) Various light-curing resin systems were prepared from a mixture (values given in mass-%) of dimethacrylates Bis-GMA (addition product of methacrylic acid and bisphenol-A-diglycidyl ether)), UDMA (addition product of 2-hydroxyethyl methacrylate and 2,2,4-trimethyl hexamethylene diisocyanate) and D.sub.3MA (decanediol-1,10-dimethacrylate) and the Ge initiators tetrabenzoyl germane (TBGe), tetrakis(2,4,6-trimethyl benzoyl)germane (TMGe) and dibenzoyl diethyl germane (DBEGe, as reference) (Table 1). The resin systems R1 and R4 (0.29 mmol/100 g) or R2, R3 and R5 (0.59 mmol/100 g) contain the same molar quantity of photoinitiator.

(15) TABLE-US-00001 TABLE 1 Composition of resins R1 to R5 Resin Component R1 R2 R3 R4* R5* TBGe 0.14 0.29 TMGe 0.39 DBEGe 0.10 0.20 Bis-GMA 42.10 42.10 42.10 42.10 42.10 UDMA 37.46 37.31 37.21 37.50 37.40 D.sub.3MA 20.30 20.30 20.30 20.30 20.30 *Comparison example

(16) Test pieces were prepared from the materials, which were irradiated twice for 3 minutes with a dental light source (Spectramat, Ivoclar Vivadent AG) and thereby cured. The flexural strength and the flexural modulus of elasticity were determined according to ISO standard IS04049 (DentistryPolymer-based filling, restorative and luting materials) after 24 h storage of the test pieces at room, temperature (RT) or after 24 h storage in water (WS) at 37 C. (Table 2).

(17) TABLE-US-00002 TABLE 2 Flexural strength (FS, MPa) and flexural modulus of elasticity (FME, GPa) of polymerized resins R1 to R5 R1 R2 R3 R4* R5* FS, RT 72.7 3.5 81.7 9.5 81.5 5.5 58.5 2.3 79.7 7.5 FS, WS 98.2 8.7 115.2 11.2 101.8 6.1 75.3 3.0 96.4 8.1 FME, RT 1.59 0.12 2.25 0.22 1.89 0.21 1.15 0.07 1.76 0.19 FME, WS 1.15 0.20 2.48 0.10 2.37 0.12 1.54 0.11 2.19 0.20 *Comparison example

(18) The results in Table 2 prove that the resins R1 and R3 with the tetra(benzoyl)germane TBGe according to the invention as photoinitiator in comparison with the reference resins R4 and R5 based on the known di(benzoyl)germane DBEGe with the same molar concentration of the photoinitiators (compare R1 with R4 or R2 with R5) lead to photopolymerisates with improved strength, and a higher modulus of elasticity.

Example 4

Preparation of Light-Curing Resins Using Tetrabenzoyl Germane (TBGe) or tetrakis(2,4,6trimethylbenzoyl)germane (TMGe) from Examples 1 and 2

(19) The composite pastes K1 to K5 were prepared from the resins R1 to R5 from Example 3 by means of a roll mill (Exakt model, Exakt Apparatebau, Norderstedt). In each case 36.44 wt. % of resins R1 to R5 were filled with 52.22 wt. % of silanized glass filler GM 27884 (1.0 m, Schott), 4.02 wt. % of silanized glass filler GM G018-056 (1.0 m, Schott), 4.02 wt. % silanized SiO.sub.2ZrO.sub.2 mixed oxide Spherosil (Transparent Materials, USA) 0.80 wt. % of silanized pyrogenic silicic acid OX-50 (Degussa) and 2.50 wt. % ytterbium trifluoride YbF.sub.3 (Sukgyung, South Korea). Analogous to Example 3, test pieces were prepared from the pastes, cured, and the flexural strength and the elastic modulus determined (Table 3).

(20) TABLE-US-00003 TABLE 3 Flexural strength (FS, MPa) and flexural modulus of elasticity (FME, GPa) of the polymerized composite pastes K1 to K5 K1 K2 K3 K4* K5* FS, RT 96.5 9.2 125.4 7.7 114.8 4.6 92.4 6.4 112 6.9 FS, WS 117.4 8.7 129.7 9.9 133.8 4.8 101.9 9.0 123.3 3.5 FME, RT 5.51 0.33 7.13 0.40 6.73 0.37 4.99 0.39 6.20 0.32 FME, WS 6.16 0.46 7.68 0.87 7.36 0.62 5.45 0.64 6.59 0.34 *Comparison example

(21) The results in Table 3 prove that the composite pastes K1 and K3 with the tetra(benzoyl)germane TBGe according to the invention as photoinitiator in comparison with the reference pastes K4 and K5 based on the known di(benzoyl) germane DBEGe with the same molar concentration of the photoinitiators (compare K1 with K4 or K2 with K5) after curing, lead to composites with an improved strength and higher modulus of elasticity.